1. Field of the Invention
The present invention relates to a flat soft magnetic material to be used in a noise-suppressing magnetic sheet, and to a process for its production.
2. Related Background Art
As the operating speeds of digital circuits have increased in recent years, the electromagnetic noise emitted from circuits has shifted more toward the high-frequency band. Such noise arises from malfunctioning of the devices themselves resulting from internal interference, or malfunctioning of other devices resulting from external interference. Further increased packaging density is also becoming necessary in recent years in order to achieve lighter-weight, thinner and smaller digital circuit-mounted devices. Electromagnetic shielding materials capable of shielding noise continue to be developed, and methods have been proposed wherein noise-suppressing parts comprising sheets of oriented and dispersed soft magnetic materials are placed near electronic circuits that are the sources of noise.
Soft magnetic materials are used in such noise-suppressing sheets, and it is known that a noise-suppressing effect can be achieved in a wide frequency band if the soft magnetic material is thin and flat.
Methods that have been disclosed for fabrication of flat soft magnetic materials include using sendust materials produced by water atomization, as a method for producing flaky or flat Fe—Si—Al alloy powder, in JP No. S62-238305 A (Document 1) and JP No. H1-294802 A (Document 2), for example. Also, JP No. 2003-332113 A (Document 3) and JP No. 2005-123531 A (Document 4) disclose using flat soft magnetic metal powders, or materials produced by gas atomization. In addition, JP No. 2001-303111 A (Document 5) discloses a method in which a fatty acid and an organic solvent such as an alcohol are included during pulverization in the mechanical flat working of a soft magnetic metal powder grinding medium by atomization using a pulverizer. Finally, JP No. H5-98301 A (Document 6) discloses, as an example, flattening treatment of sendust powder produced by water atomization together with ethanol, using an attritor.